1. Field of the Invention
The present invention relates to a sheet conveyance apparatus for conveying sheets such as recording paper or documents, an image forming apparatus, and an image reading apparatus including the sheet conveyance apparatus.
2. Description of the Related Art
Recently, an operation noise of a copying machine has been reduced by various noise countermeasures. As a result, a noise, which has been submerged before by an operation noise generated by an image forming unit in a copying machine, more specifically, a noise generated by abutting a sheet to a conveyance guide during sheet conveyance can be heard.
As such a noise, there is a noise generated when a leading edge of a sheet S collides against a conveyance guide 400 at a joining portion where one conveyance path joins with another conveyance path as illustrated in FIG. 13A. Further, as another noise, there is a noise generated when a tailing edge of the sheet S is guided in a curved conveyance path and reaches the joining portion as illustrated in FIG. 13B, because a bent sheet returns to an original state by elasticity of the sheet and hits the conveyance guide 400.
As for a countermeasure to the noise generated when a leading edge of a sheet collides against a conveyance guide at the joint part or a tailing edge collides against the conveyance guide at a time of having passed through the conveyance path, Japanese Patent Application Laid-Open No. 2008-37587 discusses a technique for providing a conveyance belt rotating in a conveyance direction at the joining portion.
However, in the conventional apparatus using the conveyance belt at the joining portion, since the conveyance belt has a function to convey the sheet in addition to a function to soften the collision, it is desired to use a high friction material having high hardness (e.g., about 60° Hs in Japan Industrial Standard A (JIS A) for the conveyance belt. If a material having low hardness is used as a material for the conveyance belt, the conveyance belt is crushed at a nip portion between the conveyance belt and a conveyance roller, so that a sheet that is being conveyed is damaged, e.g., deformation of a sheet or bending of a leading edge occurs.
However, the hardness of the conveyance belt needs to be set low for effectively reducing the noise at a time of the sheet collision. Therefore, in the apparatus using the conveyance belt at the joining portion, it has been difficult to satisfy both sheet conveyance performance and reduction of the noise generated by the sheet collision.